The present invention relates to the production of electrically conductive polymers. These polymers are derived from non-conductive base-type polymers. The electrically conductive polymers so formed are therein termed "base-type conductive" polymers. The invention is particularly concerned with novel procedures for the production of novel base-type polymers, such as conductive polyaniline, having high electrical conductivity, which do not suffer internal diffusion between conductive and non-conductile regions, do not lose conductivity on contact with water, and have good processability.
The free-base form of polyaniline is believed to comprise subunits having the formula: ##STR1## where n is between 0 and 1. The oxidation state of polyaniline referred to as "emeraldine" is believed to have a value of n of about 0.5.
The free-base form of polyaniline is electrically non-conductive. Protonic acid doping of polyaniline by reaction of polyaniline with a protonic acid HX where X is, for example, Cl, to produce electrically conductive polyaniline is known, for example, as disclosed in A. G. MacDiarmid, et al, Mol. Cryst. Liq. Cryst. 121, 173 (1985). Conductive polyaniline of this type has been employed in batteries, as disclosed, for example, in French Patent 1,519,729.
However, conductive polyaniline produced by protonic acid doping has several disadvantages. These prior art conductive materials tend toward diffusion when applied to a non-conductive dopable polymer substrate. For example, if one desires to make a conductive polyaniline trace on a non-conductive polyaniline free-bsae substrate, that trace remains conductively stable only for a very short time, after which it will start spreading until eventually the entire substrate has a constant conductivity.
Further, base-type conductive polymers, as represented by the polyaniline class of conductive polymers, have conductivities which are unstable on contact with water. Stability on contact with water is extremely rare in conducting polymers.
In addition, base-type conducting polymers, such as polyaniline, have poor processability; they tend to be somewhat insoluble powders. The few solvents that will dissolve such conductive powders are substances such as fuming sulfuric acid or aqueous formic acid, which are relatively difficult to handle and often chemically degrade the polymer. Further, if one attempts to cast a film of such conductive polymers from such solvents, they simply tend to convert either into a powder or brittle film.
An object of the present invention is the provision of improved base-type electrically conducting polymers of the class of conductive polaniline.
Another object of the invention is to provide a process for producing electrically conductive polymers, such as conductive polyaniline, which enables the physical and electrical properties on the conductive polymers to be more readily controlled.
Still another object is the provision of a novel procedure for the production of novel highly conductive base-type polymers, such as conductive polyaniline, which do not tend to diffuse when formed on a non-conductive dopable polymer substrate and which generally do not lose significant conductivity on contact with water.
Yet, another object of the invention is the production of base-type conductive polymers, such as conductive polyaniline, which have good processability characteristics.